A fire alarm informing a fire generally includes a heat detecting type fire alarm having a heat detecting element for detecting room temperature (refer to the Patent Citation 1), a smoke detecting type fire alarm having a smoke detector (refer to the Patent Citation 2), and a fire alarm having both types (refer to the Patent Citation 3 and the Patent Citation 4). The heat detecting type fire alarm determines fire generation when the temperature detected by the heat detecting element becomes high and announces an alarm as disclosed in the Patent Citation 1. On the other hand, the smoke detecting type fire alarm determines fire generation when the smoke amount detected by the smoke detector becomes large and announces an alarm as disclosed in the Patent Citation 2.
These types of fire alarms are constituted as a sensor for detecting the change in the circumference environment from fluid, the sensor having a detecting chamber constituting a detecting part measuring the temperature or the smoke amount for detecting fire. A gas alarm for executing gas detection is also constituted as a sensor for detecting the change in the circumference environment from fluid. Such a sensor measuring the environmental value by fluid is required to have a structure for guiding the fluid to be measured into the detecting part in order to accurately detect the change in the circumference environment. For this purpose, many conventional sensors have such a structure that the detecting chamber constituted as the detecting part is projected out of the housing and heated fluid or smoke to be measured is positively flown in the detecting chamber as disclosed in the Patent Citations 1 to 4.
The sensor represented in the Patent Citations 1 to 4 is constituted such that the detecting part is projected out of the housing accommodating and protecting circuit members and the like therein, whereby the detecting part is deemed to be provided in the outer environment (circumference environment to be measured). An optical type sensor for detecting smoke comprising a heat detecting element such as a thermistor, a light emitting element, or a light receiving element provided in the detecting part can execute measurement of the fluid in a condition close to the outer environment.
The conventional sensor represented by the Patent Citations 1 to 4 is explained referring to FIG. 47. FIG. 47 is a diagrammatic view showing the positional relation of the housing constituting the sensor and the detecting part for detecting the environmental value and other members are not detailed. The sensor shown in FIG. 47 is designed such that a detecting part 201 is projected out of a housing 200. A protective cover 202 covers a projected part which is the back side of the housing 200 and is opposite to the attachment portion. Namely, the detection part 201 is provided at the projected tip part covered with the protective cover 202, so that the detecting part 201 is positioned at a place closer to the circumference environment to be measured.
According to thus structured conventional sensor in FIG. 47, the detecting part 201 is provided so as to be projected out of the housing 200, so that fluid can easily flow in the detecting part 201. However, such a sensor having the projected detecting part 201 is provided in a room, it is not suitable for room design and it causes disfigurement of the room. For its purpose, a sensor has been required in these days to be smaller and thinner for improving the design appearance in the room provided with a sensor.
In order to achieve the smaller and thinner sensor, a sensor having a detecting chamber in a housing, without projecting the detecting chamber in the outer environment, is proposed like a scattered light type smoke sensor which is different from the sensor in FIG. 47 as disclosed in The Patent Citation 5. In the scattered light type smoke sensor of the Patent Citation 5, a space constituting a detecting chamber and a space for providing circuit members are divided in a housing in order to prevent incident of light into a light receiving element constituting a detection sensor.